Due to the rapid growth of 3C industries, electronic materials which can withstand high frequency and high-speed operation and has versatile multi-function are required. The printed circuit board reflects this trend by adopting thinner wiring and thickness of insulation layer, while maintaining the desired good reliability of the electronic products. Therefore, the insulation layer used must have a low dielectric constant, low dissipation factor, high glass transition temperature, and good high-temperature stability and flame retardancy.
Ball Grid Array (BGA) package technique has been developed to meet the trend of making more thinner electronic devices and high density ICs. The laminated board for BGA packaging, in addition to the basic properties required by the printed circuit board, must have the following characteristics: (1) excellent high-temperature stability, (2) high resistance to humidity, (3) high bonding strength, (4) high soldering-heat resistance, (5) flame retardancy, and (6) low dielectric constant.
P. W. Kopf, and E. R. Wagner discovered benzoxazines in the intermediates in the synthesis of phenolic resins in 1973, and H. Schreiber found out the benzoxazines can form a hard but brittle substance by self-curing upon heating in the same year (U.S. Pat. No. 2,255,504 (1973); and U.S. Pat. No. 2,323,936 (1973)). After that, many patents related to benzoxazine have been published, such as U.S. Pat. Nos. 4,501,864. 1985; 4,557,979. 1985; 5,543,516. 1996; JP 2001-106813; JP 2001-22045; JP 2001-240836; JP 2001-31095; JP 2002-145974; JP 2002-167425; JP 2003-12894; JP 2003-246844, wherein benzoxazines having two functionalities and multiple functionalities are synthesized. Benzoxazine-ring-containing compounds are stable at low temperature, and have excellent mechanical properties, high glass transition temperatures, high modulus, low moisture absorbance, low thermal expansion coefficient, high dimensional stability, and good electrical properties. Further, they can be self-polymerized in the absence of a promoter while no side products being generated. In view of these characteristics, benzoxazines are suitable for use as a high performance electronic material, and have been applied in coating, electrical laminate and encapsulant for semiconductors.
Flame retardancy is now a must to the electronic materials for more secure life safety. In order to enhance flame retardancy halogen-containing compounds or resins are added to the electronic materials as a flame retardant. Tetrabromobisphenol A is a typical example of the aromatic bromine compounds used as a flame retardant for epoxy resins. The advanced epoxy resin can be used in preparing a flame-retardant printed circuit board (FR-4) by impregnating glass fibers with the advanced epoxy resin and heating the resulting composite to cure the advanced epoxy resin. Furthermore, the advanced epoxy resin can be employed to encapsulate microelectronic devices, in which the advanced epoxy resin is cured at a high temperature with a curing agent, so that an encapsulant having a flame-retardant property is formed. Although the tetrabromobisphenol A—containing advanced epoxy resin shows flame retardant property, major problems encountered with this system are concerned with the generation of toxic and corrosive fumes during combustion such as dioxin and benzofuran. Recently, the semiconductor devices are directly soldered on the IC substrates in the fabrication of ICs, wherein that the semiconductor devices and the substrates both encounter a short period of time of high temperature (260° C., 30 sec). Further, the computing or controlling operations at high temperature are inevitable in some circumstances such as space near the car engines and summer time. Therefore, there is still a need in developing a electronic material, which is more stable at high temperature, for the fabrication of printed circuit boards and the semiconductor encapsulant.
Although benzoxazine resins have characteristics of a dihydrobenzoxazine compound contain more aryl groups and nitrogen element than general thermoset resins, which make benzoxazine resins have a better flame retardancy than other thermoset resins, but still fail to meet UL-94 V-0 level by itself. The conventional halo-containing epoxy resins or resins other than epoxy resins may be blended with the benzoxazine resins to improve the flame retardancy thereof; however, the excellent properties of the benzoxazine resins are often adversely affected.